1. Field of the Invention
This invention is related to a colorimeter and in particular, to an improved colorimeter for measuring the color of liquid in process streams.
2. Description of the Prior Art
The following prior art shows colorimeter and other color measurement devices:
U.S. Pat. No. 3,245,305 issued Apr. 12, 1966 to Turner is directed to a spectrometric apparatus with two sources of radiation, and at least one non-wavelength selective detector. The intensities of the two sources of radiation are separately measured and compared by ratioing means. The result then is used to adjust the intensity of one of the sources to maintain the intensity ratio constant.
U.S. Pat. No. 3,431,054 issued Mar. 4, 1969 to Doonan, et al, is directed to a scanning monochromator device with a broad-band spectral source that has a controlled output of radiant flux over the band of wavelengths to be scanned. The source is controlled according to an adjustable preset pattern by a variable control signal generator that varies with wavelength such that the intensity remains uniform throughout the scan.
U.S. Pat. No. 3,506,358 issued Apr. 14, 1980 to Hiroack Baba, et al. is directed to a rapid scanning double beam spectrophotometer in which a photoelectric detector is provided in each light path and the supply voltage to the detector is controlled so that the output of each detector is always at a constant level to provide for variations of intensity of light source used in the spectrophotometer.
U.S. Pat. No. 3,646,331 issued Feb. 29, 1972 to Lord is directed to a method and apparatus for correcting radiation measuring errors in a spectrophotometer. Correction factors for each discrete wavelength are stored in a computer and applied to the output of the apparatus when measurements are made.
U.S. Pat. No. 3,806,258 issued Apr. 23, 1974 to Rich is directed to an absorptionmeter in which the lamp source input power is set to a level to obtain a predetermined output; thereafter, non-wavelength selective feedback control means are provided to maintain the input lamp power at this set output level while measurements are being made.
U.S. Pat. No. 4,093,991 issued June 6, 1978 to Christie, Jr., et al. is directed to a scanning spectrophotometer-digital data processing system which includes a microcomputer.
U.S. Pat. No. 4,176,957 issued Dec. 4, 1979 to Meada, et al, is directed toward a method for optically analyzing a specimen using a double beam spectrometer having an analytical beam and a reference beam. The ratios of the intensity of the analytical and reference beams are measured when no specimen is present, then these values are applied to the corresponding reflectance measurements of a specimen to neutralize the effect of errors.
In the art of spectrophotometry, the need to correct for variations in light source intensity before accurate specimen measurements can be obtained is well recognized; however, no instrument currently exists that is able to compensate for changes in both source color temperature and spectral intensity shifts that are produced by source emission variations. In this invention, a feedback control is provided to maintain the light source at a specific predetermined color temperature and in addition compensation is made in the measurement for fluctuations in output flux of the prescribed color temperature. A further advantage of the instrument of this invention is that there is no movement of parts during the measurement phase, thus extending its serviceability.